Study On Reliability Enhancement Of Sintered Silver Against Electrochemical Migration For Electronic Packaging

Nano-silver paste has become a promising die-attach material in power semiconductor device packaging due to its excellent mechanical,thermal,and electrical properties,as well as a simple sintering process.However,silver is extremely susceptible to electrochemical migration(ECM),which could cause short circuits and failure of electronic components.With the development of wide-band-gap semiconductors in high temperature and high-density packaging,the risk of ECM would increase significantly.However,the mechanisms and methods that previously focused on improving silver migration in the normal temperature and humidity environments would be no longer applicable,which posed challenges to the reliability of high-density packaging.Some scholars have proposed adding palladium particles to nano-silver paste to improve the ECM behavior of silver,but its ECM resistance was limited and Pd was a precious metal,the cost was high,which could not meet the application requirements of large-scale commercialization and cost reduction.Therefore,there is an urgent need to explore low-cost,long-lifetime sintered silver attachment materials that can be reliably applied to high-density packaging of power devices.Firstly,based on the high-temperature ECM of sintered silver may result from the oxidation and decomposition of silver.In this paper,a suppressed idea of adding low-cost silicon-based particles with higher oxidative affinity than silver to nano-silver paste was proposed,and two kinds of nano-Ag-Si and Ag-SiO_x pastes have been prepared to connect chips by pressureless low temperature sintering.Subsequently,through comparative analysis of the ECM behavior of nano-Ag-Si paste,Ag-SiO_x paste and nano-silver paste under complex conditions of different temperatures,voltages and electrode gaps combinations,it was found that as the temperatures increased,the voltages increased,the electrode gaps decreased,the ECM failure lifetime decreased.While under the same combination of conditions,the ECM failure lifetime of sintered nano-Ag-Si and sintered nano-Ag-SiO_x was much higher than that of sintered nano-silver.Among them,the migration failure lifetime of sintered Ag-0.1%Si is 5.8 times that of sintered silver,the migration failure lifetime of sintered Ag-0.2%SiO_x is 2.6 times that of sintered silver,and the migration failure lifetime of sintered Ag-0.1%SiO_x is 1.8 times that of sintered silver.Based on the obtained lifetimes,a failure lifetime prediction model based on Arrhenius model was established to predict the failure of sintered nano-Ag-Si and sintered nano-Ag-SiO_x in actual complex operating conditions,which provided theoretical guidance for the reliability design and enhancement of high-temperature and high-density packaging of power devices.Then we explored the ECM inhibition mechanism of the sintered silver in high temperature and dry air by the addition of Si and SiO_x particles.During the ECM,due to the affinity of Si-O was higher than that of Ag-O,the formation of SiO₂ should take precedence over Ag₂O.This made Ag nanoparticles have to be oxidized after a large number of Si and SiO_x nanoparticles were completely oxidized,thence by delaying the oxidation of silver,inhibited its decomposition,ionization and migration,and ultimately the ECM failure lifetime of silver was significantly extended.Finally,the mechanical,electrical and thermal properties of sintered nano-Ag-Si and sintered nano-Ag-SiO_x connection layers were also analyzed.The results showed that although the addition of Si and SiO_x particles caused a slight reduction in the above properties,the reduction was not obvious,and all met the requirements of industrial application standards.This also further verified the feasibility of the failure suppression ideas and methods proposed in this paper.